A via is an electrical connection between wiring structures (e.g., wiring layers) in a physical electronic circuit that goes through the plane of one or more adjacent layers. For example, in integrated circuit design, a via is a small opening in an insulating oxide layer that allows a conductive connection between different wiring layers. A via connecting the lowest layer of metal to diffusion or poly is typically called a “contact”.
In via technology, a skip via can be formed through many insulator layers, e.g., bypassing one or more wiring structures within the insulator layers, to connect with a lower wiring structure. This provides improved resistance characteristics, minimizes capacitance for a lower wiring structure, e.g., at M0 layer, as well as provides area efficiencies in the chip manufacturing process.
There are many challenges to using skip vias. For example, in the manufacturing process, the skip via will land on a wiring structure in a lower level (e.g., M0 level), while the regular via will land on the wiring structure in an upper level (e.g., M1 or above level). Due to the skip via etching processes, though, damage can result at the interface between the wiring structure in the upper level and a via interconnect structure. That is, due to the different etch depths, the skip via etching process will result in surface damage to the upper wiring structure, e.g., copper (Cu) material. This damage causes higher resistivity which, in turn, decreases device performance. Further, there may be no protection for the underlying metal layer.
Metallization of the via structures, such as Cu metallization of via structures, presents other challenges. For example, during an electroless metallization, the via filling height may be different.